A liquid crystal display device including a liquid crystal panel displaying a video and a backlight device applying light to the liquid crystal panel from behind is recently widely spread for the use such as a television receiver and a displaying apparatus. In the liquid crystal display device, voltages applied to respective liquid crystal elements corresponding to pixels of the liquid crystal panel are controlled depending on a video signal and the display gradations (transmission factors) of the respective liquid crystal elements are adjusted to display video based on the video signal on the liquid panel.
To prevent motion blur and a pseudo contour generated when a moving image is displayed in the liquid crystal display device, the backlight device executes a backlight scan process of sequentially intermittently lighting light sources corresponding to respective partial areas when a display area of the liquid crystal panel is divided into a plurality of parts in conjunction with writing of a video signal to the liquid crystal elements in the partial areas in some cases (see, e.g., Patent Document 1).
FIG. 2 is a schematic of a general configuration of a backlight device 31 of a liquid crystal display device X according to an embodiment described later.
As depicted in FIG. 2, the backlight device 31 is provided with a LED light source group L30 having LED light sources L1 to L6 and a LED light source group L40 having LED light sources L7 to L12 corresponding to partial areas R50 and R60 when a display area of a liquid crystal panel 21 is vertically divided into two parts. Each of the LED light sources L1 to L12 includes a plurality of LEDs (light-emitting diodes) 31a horizontally arranged side-by-side. The backlight device 31 controls the turning on and off of the LED light sources L1 to L12 on the basis of the LED light source groups L30 and L40.
Specifically, the backlight device 31 executes the backlight scan process of sequentially intermittently lighting the LED light source groups L30 an L40 in conjunction with writing of a video signal to the partial areas R50 and R60 of the liquid crystal panel 21. A general backlight scan process will hereinafter be described with reference to FIGS. 7 to 9.
As depicted in FIG. 7, the LED light source group L30 is intermittently lit in timing that causes the LED light source group L30 to be turned on for 1/480 second, turned off for 1/240 second, and turned on for 1/480 second from the start of writing of a video signal (shaded portion) to the partial area R50 of the liquid crystal panel 21. Similarly, the LED light source group L40 is intermittently lit in timing that causes the LED light source group L40 to be turned on for 1/480 second, turned off for 1/240 second, and turned on for 1/480 second from the start of writing of a video signal to the partial area R60 of the liquid crystal panel 21.
However, as depicted in FIG. 7, an upper end area R11 and a center area R12 of the partial area R50 have different relationships between the write timing of the video signal to the liquid crystal elements and the timing of intermittent lighting of the LED light source group L30, leading to different prevention effects on a pseudo contour when a moving image is displayed. This point will hereinafter be described.
FIG. 8 depicts a relationship between the write timing of a video signal to the liquid crystal elements and the timing of intermittent lighting of the LED light source group L30 in the area R11, and FIG. 9 depicts a relationship between the write timing of a video signal to the liquid crystal elements and the timing of intermittent lighting of the LED light source group L30 in the area R12. As depicted in FIGS. 8 and 9, if an applied voltage to a liquid crystal element is varied to change the display gradation of the liquid crystal element from 100 to 128, the gradation (transmission factor) is subsequently gradually changed in the liquid crystal element. The response time of the liquid crystal element is assumed to be 1/120 second corresponding to one frame.
As depicted in FIG. 8, in the area R11, the LED light source group L30 is intermittently lit in timing that causes the LED light source group L30 to be turned on for 1/480 second (time T11 to T12), turned off for 1/240 second (time T12 to T13), and turned on for 1/480 second (time T13 to T14) from the start of writing of a video signal to the liquid crystal elements. The area R11 is provided with a turn-off period in the middle of a period from the start of a response of the liquid crystal elements until the end of the response of the liquid crystal elements and is continuously turned on for a short time of 1/480 second during the response. Therefore, the pseudo contour can effectively be prevented when a moving image is displayed in the area R11, thereby improving the moving image displaying performance.
On the other hand, as depicted in FIG. 9, in the area R12, the LED light source group L30 is intermittently lit in timing that causes the LED light source group L30 to be turned off for 1/240 seconds (time T21 to T22) and turned on for 1/240 second (time T22 to T23) from the start of writing of a video signal to the liquid crystal elements. The area R12 is continuously turned on for a longer time ( 1/240 second) during the response of the liquid crystal elements as compared to the area R11. Therefore, the prevention effect on the pseudo contour is reduced when a moving image is displayed in the area R12 as compared to the area R11.